A power management system of a drawbar machine may be designed based on a maximum machine weight and an engine torque curve. Maximum rimpull for the drawbar machine may be slip limited or power limited. In a slip limited machine, the vehicle's tires or tracks will spin if the force required to pull an implement exceeds the maximum rimpull that a vehicle can produce based on its weight and coefficient of traction. In a power limited machine, the engine will shut off before the tires or tracks spin because each gear is designed for the maximum rimpull capable by the engine.
An overload condition may occur in a slip-limited vehicle due to the effects of increased weight or weight transfer, for example, when a implement, such as a scraper or 3-point mounted implement, produces a relatively high amount of weight transfer to the drawbar machine or when extra weight is added to the vehicle for additional ballast and/or for additional fuel tanks. When the weight is increased onto the drawbar machine, the slip limit is increased, therefore increasing the designed stress levels on structural components, such as cases and frames, and powertrain components, such as gears, bearings, and shafts. When these stress levels are raised, the life of the machine may be significantly reduced, leading to customer dissatisfaction, repair costs, lost time, lost revenue, high warranty costs for the manufacturer, and/or degradation of the manufacturer's reputation.
Typically, an engine that is used in a drawbar machine is also used in other applications. Since these other applications have different requirements for the same engine, different lug curves may be certified for each application. With the advent of engine electronics, the same engine, in the same machine, can have different certified lug curves.
Some conventional engines implement a de-rating strategy in lower gears to prevent overloading by sensing the transmission gear and setting the engine to a different certified lug curve based on the gear. Using multiple certified lug curves on a drawbar machine may cause abrupt changes in rimpull, for example, a rimpull hole. A rimpull hole refers to a decrease in rimpull when downshifting that may cause the engine to lug further than normal. In addition, some of the gears may not have enough protection from the engine due to the lack of certified curves. For example, on a 300 horsepower tractor, first gear protection may require the engine to be slip limited to 150 horsepower, but the lowest certified level may be 250 horsepower, leaving first gear at risk of overload failures.
The power management system of the present invention may solve one or more of the problems set forth above.